Abstract
Bloodstream bacterial infections are life-threatening conditions necessitating prompt medical care. Rapid pathogen identification is essential for early setting of the best anti-infectious therapy. However, the bacterial load in blood samples from patients with bacteremia is too low and under the limit of detection of most methods for direct identification of bacteria. Therefore, a preliminary step enabling the bacterial multiplication is required. To do so, blood cultures still remain the gold standard before bacteremia diagnosis. Bacterial identification is then usually obtained within 24 to 48 hours -at least- after blood sampling. In the present work, the fast and direct identification of bacteria present in blood cultures is completed in less than 12 hours, during bacterial growth, using an antibody microarray coupled to a Surface Plasmon Resonance imager (SPRi). Less than one bacterium (Salmonella enterica serovar Enteritidis) per milliliter of blood sample is successfully detected and identified in blood volumes similar to blood tests collected in clinics (i.e. several milliliters). This proof of concept demonstrates the workability of our method for human samples, despite the highly complex intrinsic nature of unprocessed blood. Our label-free method then opens new perspectives for direct and faster bacterial identification in a larger range of clinical samples.
Highlights
Bacterial loads found in blood drawn from patients with bacteremia rarely exceed 10 CFU.mL−1 and are usually below 1 CFU.mL−18, 9
The sample is diluted in commercial blood culture bottles, and an aliquot (100 μL) is loaded on an antibody microarray for real-time Surface Plasmon Resonance imager (SPRi) monitoring during enrichment
With the increasing occurrence of multidrug resistant bacterial strains, the early detection of bacteria in clinics is a crucial issue in terms of patient validated prognosis and healthcare cost control
Summary
Bacterial loads found in blood drawn from patients with bacteremia rarely exceed 10 CFU.mL−1 and are usually below 1 CFU.mL−18, 9. Based on the high bacterial concentrations obtained after enrichment, as positive blood cultures usually contain at least 107–108 CFU.mL−115, 16, bacteria identification may be led on culture supernatants using MALDI TOF mass spectrometry[17, 18] or other automated molecular methods[19]. Such approaches are promising but still need to be further improved to better detect some bacterial strains. Nucleic-acid-based methods may be performed on positive blood culture supernatants after enrichment, with a processing time generally shorter than 2 hours and good sensitivity and specificity values These label-based molecular techniques remain labor-intensive and expensive. Some PCR-based methods have been directly applied to unprocessed blood samples, but showed
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